Fuel additives

ABSTRACT

The emission of particulates and unburnt hydrocarbons in the exhaust gas emissions from liquid hydrocarbon fuels, especially diesel fuels and fuel oils is reduced by incorporating into the fuel an effective amount of an oil-soluble alkali, alkaline earth or rare earth complex of the formula: 
     
         M(R).sub.m.nL 
    
     wherein M is the metal cation of valency m, R is the residue of an organic compound RH containing an active hydrocarbon atom, preferably a beta-diketone, n is an integer usually 1, 2, 3 or 4, and L is an organic donor ligand molecule, i.e., a Lewis base.

This invention relates to additives for liquid hydrocarbon fuels, andfuel compositions containing them. More specifically the inventionrelates to additives effective to reduce the particulate and/or unburnthydrocarbon content of exhaust gas emissions from distillate hydrocarbonfuels such as diesel and heating oils.

Diesel fuels and diesel engines are particularly prone to the emissionof small size particulate material in the exhaust gas, and theseparticulates are known to contain harmful pollutants. These particulatesinclude not only those which are visible as smoke emission, and to whichdiesel engines are prone especially when the engine is overloaded, worn,badly maintained or quite simply dirty, but also those which emerge fromlightly loaded, clean diesel engines and which are normally invisible tothe naked eye.

As indicated, particulate emission by diesel engines is a major sourceof harmful atmospheric pollution, and an effective particulatesuppressant for diesel fuels is highly sought after.

Similar problems can also arise during the combustion of otherdistillate fuel oils, e.g. heating oils.

Yet another problem associated with liquid hydrocarbon fuels of allkinds is that of incomplete combustion (which is largely responsible forsoot formation anyway) resulting in the emission of unburnt hydrocarbonsinto the atmosphere as an atmospheric pollutant. A need exists thereforefor additives effective to reduce the content of unburnt hydrocarbon inthe exhaust gas emissions from liquid hydrocarbon fuels.

In the proceedings of the Nineteenth Symposium (international) onCombustion, 1983, p. 1379, published by the Combustion Institute, Haynesand Jander have disclosed that alkali and alkaline earth metals canreduce sooting in premixed hydrocarbon flames.

More specifically related to diesel engines, proposals have been madeconcerning the use of rare earth metals to reduce particulate emissionsby diesel engines, see, for example, U.S. Pat. Nos. 4,522,631, 4,568,357and 4,968,322.

In U.S. Pat. No. 4,522,631 particulate emission from diesel fuel isreduced by adding to the fuel prior to combustion, an additivecomposition comprising the combination of an oxygenated organiccompound, e.g. alcohol, aldehyde, ketone or alkylcarbitol, preferablyn-hexylcarbitol, and an oil-soluble rare earth compound, preferably acerium carboxylate salt such as cerium octanoate.

In U.S. Pat. No. 4,568,357 a combination of manganese dioxide and cerium(III) naphthenate is added to diesel fuels to facilitate theregeneration of ceramic particulate traps used with diesel engines toentrap particulates in the exhaust gas, and which traps require periodicregeneration by burning off the trapped particulates. The manganeseoxide and cerium naphthenate act synergistically to lower the burn-offtemperature required to effect the regeneration of the trap. The U.S.Pat. No. 4,568,357 patent does not suggest that the cerium compound iseffective to reduce particulate emission in the first place.

In U.S. Pat. No. 4,968,322 a combination of rare earth metal soapspreferably selected from a cerium soap, a neodymium soap and a lanthanumsoap, are added to heavy fuel oils to improve the combustion rate of thefuel.

Other attempts to reduce particulate emission from diesel fuels, mostlybased on calcium and barium soaps have been reported in U.S. Pat. Nos.2,926,454, 3,410,670, 3,413,102, 3,539,312 and 3,499,742.

In addition to the foregoing, oil-soluble chelates of Ce(IV) such asceric 3,5-heptanedionate, have been proposed as antiknock compounds ingasoline fuels for use in spark ignition internal combustion engines asan alternative to lead tetraalkyls such as tetraethyllead andtetramethyllead, see U.S. Pat. No. 4,036,605. However there is nosuggestion that such chelates have any particulate suppressant activityin diesel fuels.

Other metals such as copper, manganese and iron have also beenconsidered but give rise to other environmental concerns and/or concernsregarding damage or wear to the engine itself.

In accordance with the present invention it has been found that variousorganometallic coordination complexes of alkali, alkaline earth and rareearth metals, including mixtures thereof, are effective particulatesuppressants for liquid hydrocarbon fuels, especially distillatehydrocarbon fuels such as diesel and fuel oil, besides providing anumber of added advantages such as high solubility and dispersibility inthe fuel, good thermal stability and good volatility.

A particular advantage of such complexes is their low nuclearity, manybeing monomeric in character, although some are dimeric or trimeric, orhigher. This low nuclearity means that, in contrast to metallic soaps,the traditional method of providing oil-soluble metallic compounds, thecomplexes used in accordance with the present invention provide auniform distribution of metal atoms throughout the fuel, each metal atomtheoretically being available to take part in whatever mechanism it isthat results in the reduction of particulate emission when the fuel isburned, this availability being enhanced moreover by the volatility ofthe complexes. This is in complete contrast to the metallic soaps, whichconsist essentially of individual micelles containing an unknown numberof metal, e.g. alkali or alkaline earth metal, cations surrounded by ashell of acid groups derived from a long chain fatty acid or alkylsulphonic acid bound to the metal atoms on the surface of the particle.Whilst such soaps are oil-soluble, the metal will not be uniformlydispersed throughout the fuel as individual atoms, but as clusters eachsurrounded by a shell of fatty acid or alkylsulphonate molecules. Notonly that, but only a limited number of metal atoms are available on thesurface of the micelle for reaction, so the effectiveness of those soapsis low. Moreover, since the soaps are non-volatile there is asignificant risk of increased deposit formation in the engine itself andin the fuel injectors, including the fuel injectors of oil-fired boilersetc., quite apart from the fact that the combustion process is a vapourphase reaction, essentially requiring the particulate suppressant itselfto be volatile in order to have any effect.

Whilst the reasons for beneficial effect of the present coordinationcomplexes as particle suppressants in liquid hydrocarbon fuels is notunderstood, it is probable that this is due to catalytic oxidationactivity of the metal atoms adsorbed onto soot particles formed duringthe combustion process and effective to catalyse the oxidation of thoseparticles and thus to effect their removal from the exhaust gas stream,either directly or in conjunction with catalytic or trap devices.However, that is speculation, and the mode of action of the complexes asparticle suppressants in hydrocarbon fuels in accordance with thisinvention is not important.

In one aspect of the present invention, therefore, there is provided aparticulate suppressant additive for liquid hydrocarbon fuels comprisingan organic, fuel-soluble carrier liquid, preferably hydrocarbon,miscible in all proportions with the fuel, and containing therein acoordination complex of an alkali, alkaline earth or rare earth metalsalt, such complex being of the general formula

    M(R).sub.m.nL

where M is the cation of an alkali metal, alkaline earth metal or rareearth metal of valency m;

R is the residue of an organic compound of the formula RH where Hrepresents an active hydrogen atom reactive with the metal M andattached either to a heteroatom selected from O, S and N in the organicgroup R, or to a carbon atom, that hetero or carbon atom being situatedin the organic group R close to an electron-withdrawing group, e.g. aheteroatom or group consisting of or containing O, S, or N, or aromaticring e.g. phenyl, but not including active hydrogen atoms forming partof a carboxyl (COOH) group;

n is a number indicating the number of donor ligand molecules formingdative bonds with the metal cation in the complex, usually up to five innumber, more usually an integer of from 1-4, but can be zero when M is arare earth metal; and

L is an organic donor ligand (Lewis base).

In a second aspect, there is provided a fuel containing, as an exhaustgas particulate suppressant, a Lewis base complex as above defined andin an amount sufficient to provide in the fuel from 0.1-500 ppm of themetal M, preferably from 0.1 to 100 ppm, most preferably 0.5 to 50 ppm.

In a different but related aspect of the present invention, it has alsobeen found that in addition to particulate suppression, the additivecompositions of this invention containing one or more complexes of theformula M(R)_(m).nL, lead to reduction in unburnt hydrocarbon emission,not only in the exhaust gas emissions from diesel fuels but from otherliquid hydrocarbon fuels as well. Not only that, but the additives alsoserve to remove preformed soot or carbon deposits in internal combustionengines and fuel injectors of all kinds, including exhaust systems usedtherewith. Whilst no definitive explanation can yet be given for this,it is suspected that these phenomena are due in part to oxidativecatalytic activity of the complex (or to a thermal decomposition productthereof) effective to increase the combustion rate of the fuel andincrease the burn off rate of predeposited carbon and soot. Thus inaddition to particulate suppression, the additive compositions of thisinvention have added value as exhaust emission control agents forreducing unburnt hydrocarbon emissions from liquid hydrocarbon fuels,and as clean-up agents for the removal of soot and carbon depositsresulting from the incomplete combustion of liquid hydrocarbon fuels.Amounts of metal complex(es) added to the fuel for these purposes willgenerally be the same as before, i.e. sufficient to provide aconcentration of the metal or metals M in the fuel in the range 0.1 to500 ppm, preferably 0.1 to 100 ppm, most preferably 0.5 to 50 ppm.

In yet another aspect of the invention therefore there is provided amethod of reducing the unburnt hydrocarbon emission of liquidhydrocarbon fuels when combusted, which comprises incorporating into thefuel prior to combustion an alkali, alkaline earth or rare earth metalcomplex of the formula given above, or a mixture of two or more suchcomplexes in an amount sufficient to provide in said fuel from 0.1 to500 ppm, preferably 0.1 to 100 ppm of the metal(s) M.

In yet another aspect of the invention them is provided a method ofreducing carbon deposits resulting from the incomplete combustion ofliquid hydrocarbon fuels, which comprises incorporating into the fuelprior to combustion an alkali, alkaline earth or rare earth metalcomplex of the formula given above, or a mixture of two or more suchcomplexes, in an amount sufficient to provide in said fuel from 0.1 to500 ppm, preferably 0.1 to 100 ppm of the metal(s) M.

Referring in more detail to the Lewis base metallo-organic coordinationcomplexes used in accordance with the invention, these are, asindicated, Lewis base coordination complexes of alkali metals, alkalineearth metal and rare earth metal salts of organic compounds containingan "active" hydrogen atom reactive with and replaceable by the metalcation. In the organic compound RH, that active hydrogen atom will beattached to a heteroatom (O, S or N) or to a carbon atom close to anelectron-withdrawing group. That electron withdrawing group may be ahetero atom or group consisting of or containing O, S or N, e.g. acarbonyl (>C═O), thione (>C═S) or imide (>C═NH) group, or an aromaticgroup, e.g. phenyl. When that electron-withdrawing group is a heteroatom or group, that hetero atom or group may be situated in either analiphatic or alicyclic group, which, when the active hydrogen containinggroup is an >NH group, may or may not, but usually will contain thatgroup as part of a heterocyclic ring. Preferably theelectron-withdrawing group is in the α-position relative to the atomcontaining the active hydrogen, although it may be further away, theessential requirement being that in the crystalline complex, thatelectron-withdrawing group is sufficiently close to the metal cation toform a dative bond therewith. The preferred organic compounds, RH, arethose in which the active hydrogen atom is attached to a carbon atom inthe organic group R, especially an aliphatic carbon atom situated in analiphatic chain between two carbonyl groups, that is to say aβ-diketone.

Especially preferred are complexes derived from a β-diketone of theformula

    R.sup.1 C(O)CH.sub.2 C(O)R.sup.1

where R¹ is C₁ -C₅ alkyl or substituted alkyl, e.g. halo-, amino- orhydroxyalkyl, C₃ -C₆ cycloalkyl, benzyl, phenyl or C₁ -C₅ alkylphenyl,e.g. tolyl, xylyl, etc., the two R¹ groups being the same or different.

Suitable β-diketones include acetyl acetone: CH₃ C(O)CH₂ C(O)CH₃,hexafluoroacetylacetone (HFA): CF₃ C(O)CH₂ C(O)CF₃, hepta-3,5-dione: C₂H₅ C(O)CH₂ C(O)C₂ H₅, 2,2,6,6-tetramethylhepta-3,5-dione (TMHD): (CH₃)₃CC(O)CH₂ C(O)C(CH₃)₃ etc., etc.

When, in the organic compound RH, the active hydrogen atom is attachedto oxygen, suitable compounds include phenolic compounds containing from6-20 carbon atoms, preferably substituted phenols containing from 1-3substituents selected from alkyl, aminoalkyl, alkylaminoalkyl, andalkoxy groups of 1-8 carbon atoms, e.g. cresol, guiacol,di-t-butylcresol, dimethylaminomethyl cresol etc. The substitutedphenols are particularly preferred.

When the active hydrogen is attached to a nitrogen atom in the organiccompound RH, the preferred compounds are heterocyclic compounds of up to20 carbon atoms containing a --C(Y)--NH--group as part of theheterocycle, Y being either O, S or ═NH. Suitable such compounds aresuccinimide, 2-mercaptobenzoxazole, 2-mercapto-pyrimidine,2-mercaptothiazoline, 2-mercaptobenzimidazole, 2-oxobenzazole, etc.,etc.

As to the organic ligand L, any suitable organic electron donor (Lewisbase) may be used, the preferred organic electron donors (Lewis bases)being hexamethylphosphoramide (HMPA), tetramethylethylenediamine(TMEDA), pentamethyldiethylenetfiamine (PMDETA), dimethylpropyleneurea(DMPU) and dimethylimidazolidinone (DMI). Other possible ligands arediethylether (Et₂ O), 1,2-dimethoxyethane, bis(2-methoxyethyl)ether(diglyme), dioxane, and tetrahydrofuran. It is, however, to beunderstood that this listing is by no means exhaustive and othersuitable organic ligands (Lewis bases) will suggest themselves topersons skilled in the art. The alkali metal and alkaline earth metalcomplexes will usually contain from 1 to 4 ligand molecules to ensureoil solubility, i.e. the value of n will usually be 1, 2, 3 or 4. In thecase of the rare earth metal complexes, the organic groups R maythemselves provide sufficient oil solubility to the extent that N can beand often is 0.

The Lewis base metallo-organic salt complexes used in the invention areobtained by reacting a source of the metal M, e.g. the elemental metal,a metal alkyl or hydride, an oxide or hydroxide, with the organiccompound RH in a hydrocarbon, preferably aromatic hydrocarbon solventsuch as toluene, containing the ligand in the stoichiometric amount orin excess of stoichiometric. Where a metal oxide or hydroxide is used,the reaction proceeds via the route described in more detail in GB-A-2254 610. In that case the initial product of the reaction is anaquo-complex of the formula M(R)_(m).nL.xH₂ O containing water as aneutral ligand as well as the donor ligand (L). In that formula M, R, m,and L are as above defined and x is 1/2,1, 11/2, 2 etc., usually 1 or 2.Those aquo-complexes can be recovered in crystalline form from thereaction solution and heated to drive off the neutral ligand, i.e. thewater molecules, leaving the anhydrous complex M(R)_(m).nL. The abovereactions and preparative routes are illustrated by equations: ##STR1##

It will be appreciated that the above routes will not be equallyapplicable to all the metals M nor to all organic compounds RH. Theparticular route shown will depend on the materials used, and especiallythe availability of a suitable source of the metal M. For this reasonalone, the most suitable route will usually be either route i) or routeii) indicated above, since the most convenient source of the metal Mwill usually be the oxide or hydroxide.

Whilst it has already been indicated that the structure of many of thecomplexes is monomeric, crystallographic studies show some of them to bedimeric or trimeric in structure. This gives rise to the possibilitythat, within the crystal lattice one metal atom may be replaced byanother, different metal atoms giving rise to mixed metal complexes ofthe general formula indicated, i.e. M(R)_(m).nL, but where within thecrystal structure of the complex M represents two or more differentmetals. Techniques for the manufacture of such mixed metal complexes aredescribed in GB-A-2 259 701. Such mixed metal complexes, i.e. where M inthe formula of the complex represents two or more different alkali,alkaline earth or rare earth metals, are therefore to be included withinthe scope of that formula, and within the scope of the presentinvention, as are, of course, mixtures of two or more differentcomplexes.

Whilst any of the alkali (Group Ia; At. Nos. 3, 11, 19, 37, 55),alkaline earth (Group II; At. Nos. 4, 12, 20, 38, 56) or rare earth (At.Nos. 57-71 inclusive) metals may be used as the metal (or metals) M,preferred are the donor ligand complexes of sodium, potassium, lithium,strontium, calcium and cerium.

Whilst the metallo-organic salt complexes described herein as smokesuppressants for liquid hydrocarbon fuels may be added directly to thefuel in amounts sufficient to provide from 0.1 to 500 ppm, preferably0.1 to 100 ppm, of the metal M in the fuel, they will preferably firstbe formulated as a fuel additive composition or concentrate containingthe complex, or mixtures of the complex possibly along with otheradditives, such as detergents, antifoams, stabilisers, corrosioninhibitors, cold flow improvers, antifreeze agents, cetane improvers asis well known in the art, in solution in an organic carrier liquidmiscible with the fuel. Suitable carrier liquids for this purposeinclude: aromatic kerosene hydrocarbon solvents such as Shell Sol AB(boiling range 186° C. to 210° C.), Shell Sol R (boiling range 205° C.to 270° C.), Solvesso 150 (boiling range 182° C. to 203° C.), toluene,xylene, or alcohol mixtures such as Acropol 91 (boiling range 216° C. to251° C.). Other suitable carrier liquids miscible with diesel and othersimilar hydrocarbon fuels and fuel will be apparent to those of ordinaryskill in the art. Concentrations of the metal complex in the additivecomposition may be as high as 50% by weight, calculated as the metal M,but will more usually be from 0.1 to 20% by wt. of the metal M mostusually from 0.5 to 10%.

By "diesel fuel" herein is meant a distillate hydrocarbon fuel forcompression ignition internal combustion engines meeting the standardsset by BS 2869 Pans 1 and 2. The corresponding standard for heating oilsis BS 2869 Part 2.

The invention is illustrated by the following examples and test data.

EXAMPLE 1 Preparation of the 1,3-dimethylimidazolidinone (DMI) Complexof strontium bis-2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD):Sr(TMHD)₂. 3DMI

2,2,6,6-tetramethyl-3,5-heptanedione, (CH₃)₃ CC(O)CH₂ C(O)C(CH₃)₃, TMHD(18.54 g, 21 ml, 100.6 mmol) was syringed into a stirred, cooled mixtureof dimethylimidazolidinone, ##STR2## DMI (32.32g, 30ml, 283 mmol) intoluene (20 ml) with a strontium metal lump (ca 6 g, 68 mmol). Themixture was then heated and stirred overnight. The solids which formedwere dissolved by adding a further 30 ml of toluene, and then the liquidwas filtered and cooled. After several hours, a crystalline productformed which was washed with hexane, isolated and identified as thetris-1,3-dimethylimidazolidinone complex of strontiumhis-2,2,6,6-tetramethyl -3,5-heptanedionate.

Formula: Sr[(CH₃)₃ CC(--O)═CHC(═O)C(CH₃)₃ ]₂.3DMI, Mw 797

Yield: 23 g, first batch, 58% based on TMHD and on a 2/3 ligand: donorratio.

m.p.: 82° C. sharp, to a clear colourless liquid.

    ______________________________________                                        Elemental analysis (%)                                                                     Found Theory                                                     ______________________________________                                        Sr             10.99   10.6                                                   C              56.14   55.7                                                   H              8.7     8.6                                                    N              10.3    10.3                                                   ______________________________________                                    

Thermal Analysis

STA

The compound gives a two stage weight loss profile. The first loss,presumably the DMI ligands, are lost steadily from 120° C. to 270° C.followed by what is thought to be volatilisation of the uncomplexedcompound from 270°-390° C. leaving a minimal residue (2%) by 400° C.

DSC

A sharp melting point is seen to occur at 82° C. implying a highly purematerial.

EXAMPLE 2 Preparation of the 1,3-dimethylimidazolidinone (DMI) complexof potassium 2,2,6,6-tetramethyl-3,5-heptanedionate: K TMHD.2DMI

KH (0.90 g, 22.5 mmol) was washed with mineral oil, dried and placed ina Schlenk tube. Hexane was then added followed by DMI (7 ml, 64.22mmol). Tetramethylheptanedione (4.4 ml, 21.05 mmol) was then addedslowly, as a very vigorous reaction takes place. After about fifteenminutes the reaction subsided and an oil settled out of solution. Thetwo-phase liquid was cooled in an ice-box (-10° C.) and some solidcrystalline mass formed from the oil pan over half an hour.

The crystalline solids were washed with hexane, isolated and determinedto be the bis-1,3-dimethylimidazolidinone (DMI) complex of potassium2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD).

Formula: K[(CH₃)₃ CC(--O)═CHC(═O)C(CH₃)₃ ].2 DMI, Mw 451

Yield: 1.7 g, 16% first batch based on a 1/2 ligand:donor ratio

    ______________________________________                                        Elemental Analysis (%)                                                                       Found   Theory                                                 ______________________________________                                        K              9.9     8.68                                                   ______________________________________                                    

Thermal Analysis:

STA

A fairly flat curve is seen from ambient to around 270° C. then anapparent one step weight loss occurs until by around 390° C. a smallresidue remains.

DSC

This shows a fairly wide melting range, peaking at 76° C. and isfollowed by a sharp endothermic event at 119° C.

EXAMPLE 3 Preparation of the 1,3-dimethylimidazolidinone (DMI) complexof calcium 2,2,6,6-tetramethyl-3,5-heptanedionate: CaTMHD₂.2DMI

Calcium hydride (0.42 g, 10.0 mmol) was placed in a Schlenk tube andDMI, (2.2 ml, 20 mmol), toluene (10 ml) and TMHD (4.2 ml, 20.0 mmol)added. The mixture was sonicated for half an hour and then heated andstirred at 90° C. overnight. A powder gradually formed in the solution,and subsequently a thick, solid mass. Addition of toluene to the solidcaused it to dissolve. The mixture was filtered then placed in a fridge.A crop of crystals was produced and determined to be the bis-DMI complexof Ca(TMHD)₂.

Formula: Ca[(CH₃)₃ CC(--O)═CHC(═O)C(CH₃)₃ ]₂. 2DMI, Mw 635

Yield: 3.6 g, 1st batch 56%.

    ______________________________________                                        Elemental Analysis (%)                                                                     Found Theory                                                     ______________________________________                                        Ca             6.7     6.3                                                    C              60.16   60.26                                                  H              9.71    9.18                                                   N              8.28    8.83                                                   ______________________________________                                    

Thermal Analysis

STA

The experiment showed that the compound was stable to just below itsmelting point, then ligand was lost till 275° C. when the rest of theresidue volatilised.

DSC

Showed one very sharp melting point at 118° C.

EXAMPLE 4 (cancelled) EXAMPLE 5 Preparation of the1,3-dimethylimidazolidinone (DMI) complex of sodium 2-methoxyphenoxide

2-Methoxyphenol [HOC₆ H₄ (2-OCH₃)](4.92 g, 4.50 ml, 40.0 mmol) was addedslowly to a suspension of Nail (0.96 g 40.0 mmol) in DMI (4.56 g, 5.5ml, 40.0 mmol) and toluene (40 ml). An exothermic reaction occurred anda clear straw coloured solution was the result. Refrigeration overnightcaused a large batch of small crystals to form.

The crystals were washed, dried and determined to be the DMI adduct ofsodium 2-methoxyphenoxide.

Formula: Na[OC₆ H₄ (OCH₃) DMI, Mw 260

Yield: 7.8 g first batch 75% based on a 1/1 ratio.

m.p.: 87°-89° C. to a clear colourless liquid.

    ______________________________________                                        Elemental Analysis (%)                                                                     Found Theory                                                     ______________________________________                                        Na             8.4     8.8                                                    C              54.5    55.5                                                   H              6.6     6.5                                                    N              10.9    10.7                                                   ______________________________________                                    

EXAMPLE 6 Preparation of the 1.3-dimethylimidazolidinone (DMI) complexof lithium 2,6,-di-t-butyl-4-methylphenoxide

BuLi (7.5 ml of a 2M solution in cyclohexane, 15.0 mmol) was added to2,4-di-t-butyl-4-methylphenol (3.4 g, 15.5 mmol) and DMI (5.5 ml, 50.0mmol). A thick white precipitate was obtained which was warmed anddissolved by addition of DMI. Cooling on line followed by refrigerationcaused crystallisation.

The crystalline solids were washed with hexane, isolated and determinedto be the 1,3-dimethylimidazolidinone complex of lithium2,6-di-t-butyl-4-methylphenoxide.

Formula: LiOC₆ H₂ [2,6-C(CH₃)₃ ]₂ (4-CH₃).DMI, Mw 340.5

Yield: 2.8 g, 55% first batch.

m.p.: 285° C.

    ______________________________________                                        Elemental Analysis (%)                                                                     Found Theory                                                     ______________________________________                                        Li             2.81    2.84                                                   C              66.38   70.6                                                   H              9.48    9.7                                                    N              7.54    8.2                                                    ______________________________________                                    

EXAMPLE 7 Preparation of the 1,3-dimethylimidazolidinone (DMI) complexof lithium 2,2,6,6-tetramethyl-3,5-heptanedionate: LiTMHD.2DMI

BuLi (75 ml of a 1.6 molar solution in hexane, 0.12 mol) was syringedinto a two neck flask under nitrogen. A mixture of TMHD (24.98 ml, 22.1g, 0.12 mol) and DMI (30 ml, 31.2 g, 0.24 mol) 2 equivalents with hexane(30 ml) were then slowly dripped into the stirred uncooled solution.

The solution became yellow then lightened as the reaction reached theend. Solids then formed which went back into solution and the liquid wasallowed to cool to yield a crystalline product. This was redissolved bygentle heating in an oil bath. Hexane (30 ml) was added and the solutioncooled once more. The material which re-crystallised was identified asthe DMI complex of LiTMHD.

Formula: Li[(CH₃)₃ CC(--O)═CHC(═O)C(CH₃)₃ ].2DMI, Mw 419

Yield: 32 g, 64% first batch

m.p.: 89°-90° C.

    ______________________________________                                        Elemental Analysis (%)                                                                       Found   Theory                                                 ______________________________________                                        Li             1.65    1.67                                                   ______________________________________                                    

EXAMPLE 8 Preparation of the 1,3-dimethylhnidazolidinone (DMI) complexof sodium 2,2,6,6tetramethyl-3,5-heptanedionate: Na TMHD.2DMI

This complex was prepared using similar methods to Example 2 but withsodium hydride in place of potassium hydride.

Formula: Na[(CH₃ 3)₃ CC(--O)═CHC(═O)C(CH₃)₃ ].2DMI, Mw 435

m.p.: 71°-72° C.

EXAMPLE 9 The preparation of the 1,3-dimethylimidazolidinone (DMI)complex of caesium 2,2,6,6-tetramethyl-3,5-heptanedionate: (TMHD): CsTMHD.0.2 DMI

An ampoule of caesium (2 g, 15.0 mmol), was placed in a Schlenk tube andcovered by THF (90 ml). TMHD (3.2 ml, 15.0 mmol) was then added, thetemperature controlled to 60° C. and the reaction mixture stirredover-night. A clear yellow solution was obtained. The empty ampoule wasremoved, and the solution cooled to ambient temperature. All the solventwas then removed to obtain a white solid. Hexane was added (40 ml) andDMI (4 ml) was syringed into the tube to cause dissolution. The liquidwas then refrigerated to -20° C.

After two hours a batch of white crystalline material formed, which wasthen filtered, washed with hexane and isolated. This was identified as aDMI (0.2 equivalent) adduct of CsTMHD.

Formula: Cs[(CH₃)₃ C(--O)═CHC(═O)C(CH₃)₃ ].0.2DMI, Mw 342

Yield: 2.3 g first batch, 45%

m.p.: 182°-184° C.

    ______________________________________                                        Elemental Analysis (%)                                                                     Found Theory                                                     ______________________________________                                        C              42.03   41.8                                                   H              6.05    6.02                                                   N              2.57    2.5                                                    ______________________________________                                    

EXAMPLE 10 Preparation of rubidium2,2.6,6-tetramethyl-3,5-heptanedionate

This compound was made under similar conditions to those specified inExample 10, using an ampoule of rubidium in place of caesium, but on a23.0 mmol scale.

Formula: Rb[(CH₃)₃ CC(--O)═CHC(═O)C(CH₃)₃ ], Mw 268.7

    ______________________________________                                                     Found Theory                                                     ______________________________________                                        C              48.77   49.1                                                   H              7.67    7.1                                                    ______________________________________                                    

EXAMPLE 11 Preparation of the 1,3-dimethylimidazolidinone (DMI) complexof:potassium 2,6di-t-butyl-4methylphenoxide

This complex was made using potassium hydride in place of BuLi in asimilar work up to Example 6, but on a 20.0 mmol scale.

Formula: KOC₆ H₂ [2,6-C(CH₃)₃ ]₂ (4-CH₃).2DMI, Mw 486

Yield: 5.3 g, 57%

m.p.: 92°-96° C.

    ______________________________________                                        Elemental Analysis (%)                                                                     Found Theory                                                     ______________________________________                                        K              8.17    8.02                                                   C              60.91   61.7                                                   H              8.87    8.85                                                   N              11.42   11.52                                                  ______________________________________                                    

EXAMPLE 12 Preparation of the 1,3-dimethylimidazolidinone (DMI) complexof lithium 2,4,6-trimethylphenoxide

A similar route was used to that of Example 6, but using2,4,6-trimethylphenol in place of 2,6-di-t-butyl-4-methylphenol, but ona 90 mmol scale reaction.

Formula: LiOC₆ H₂ (2,4,6-CH₃)₃.1.5DMI, Mw 313

Yield: 14.8 g, 52%

m.p.: 115° C.

    ______________________________________                                        Elemental Analysis (%)                                                                       Found   Theory                                                 ______________________________________                                        Li             2.2     2.2                                                    ______________________________________                                    

EXAMPLE 13 Preparation of the 1,3-dimethylimidazolidinone (DMI) complexof strontium bis-2,4,6-trimethyiphenoxide

Strontium metal (4.5 g, excess) and 2,4,6-tri-methylphenol (5.44, 40.0mmol) were reacted together in DMI (10 ml, ca. 90.0 mmol) and toluene(100 ml) with heat. Filtering and removal of solvent gave a batch ofcrystals.

Formula: Sr[OC₆ H₂ (2,4,6-CH₃)₃ ]₂.5DMI, Mw 929.02

Yield: 12 g, 49%

m.p.: 244° C.

    ______________________________________                                        Elemental Analysis (%)                                                                     Found Theory                                                     ______________________________________                                        Sr             9       9.4                                                    C              53.8    55.6                                                   H              7.3     7.7                                                    N              15.2    15.1                                                   ______________________________________                                    

EXAMPLE 14 Preparation of lithiumN,N-dimethyl-2-aminomethylene-4-methylphenoxide

N,N-Dimethyl-2-aminomethylene-4-methylpheno1 (11.5 g, 57.8 mmol as 97.3%pure), was added slowly to n-BuLi (44 ml of a 1.6M solution in hexane,70.25 mmol) in toluene (30 ml). A very exothermic reaction occurred andthe mixture was cooled whilst addition was taking place. A clear strawcoloured solution resulted, which was continually stirred until thetemperature dropped to ambient. Solvent was next removed until a whiteprecipitate formed. From which recrystallisation from hexane byrefrigeration (12 h) caused large pyramidal crystals to form.

The crystals, which needed to be filtered cold, were washed, dried anddetermined to be lithiatedN,N-dimethyl-2-aminomethylene-4-methylphenoxide.

Formula: LiOC₆ H₃ [2-CH₂ N(CH₃)₂ ](4-CH₃), Mw 171

Yield: 8.4 g, yield 72%.

m,p.: 252°-255° C. to a clear colourless liquid.

    ______________________________________                                        Elemental Analysis (%)                                                                    Found  Theory                                                     ______________________________________                                        C             70.58    70.18                                                  II            8.78     8.19                                                   N             8.22     8.19                                                   Li            4.05/4.04                                                                              4.09                                                   ______________________________________                                    

EXAMPLE 15 Preparation of ceriumtetrakis-2,2,6,6-tetramethyl-3,5-heptanedionate: CeTMHD₄

Cerium chloride, CeCl₃ (5.19 g, 21.0 mmol), was placed in a conicalflask with a 50% ethanolic solution (100 ml).

In a second flask sodium hydroxide (60.0 mmol) in ethanol (50 ml) wasreacted with TMHD (12.5 ml, 60.0 mmol), and this product was addedslowly using a dropping funnel to the Ce solution suspension. A redsolid in a cloudy solution was obtained. Hexane (150 ml) was added todissolve organically soluble products and this layer was thentransferred to a Schlenk tube after filtration and the liquids removedunder vacuum.

A deep red solid was precipitated, dried and collected and determined tobe cerium tetrakis-2,2,6,6-tetramethyl-3,5-heptanedionate.

Formula: Ce[(CH₃)CC(--O)═CHC(═O)C(CH₃)₃ ]₄, Mw 873.24

Yield: 8.7 g, 17%

m.p.: 276°-277° C.

    ______________________________________                                        Elemental Analysis (%)                                                                   Found    Theory                                                    ______________________________________                                        C            60.93      60.5                                                  H            8.76       8.7                                                   Ce           16 (by SEM)                                                                              16.06                                                 ______________________________________                                    

EXAMPLE 16 Preparation of ceriumtetrakis-2,2,7-trimethyl-3,5-octanedionate: Ce(TOD)₄

This compound was prepared in a similar way to Example 8, except that asodium precursor of trimethyloctanedione, TOD, was used to prepare thecompound identified as Ce TOD₄.

Formula Ce[(CH₃)₃ CC(--O)═CHC(═O)CH₂ CH(CH₃)₂ ]₄ Mw 873.24

m.p.: 145° C.

    ______________________________________                                        Elemental Analysis (%)                                                                     Found Theory                                                     ______________________________________                                        C              60.93   60.5                                                   H              8.76    8.7                                                    ______________________________________                                    

TEST DATA

Static Engine Tests

The above described strontium and calcium complexes were added to a testdiesel fuel in amounts sufficient to provide metal concentrations of 1.5milligram atoms per kg. of fuel and tested for smoke emission in astatic Perkins 236 DI single cylinder research engine. The fuel used wasa standard European legislative reference diesel fuel, CEC RO3-A84. Theblend data were as follows:

                  TABLE 1                                                         ______________________________________                                                Metal                      Metal Metal                                Metal   Automic  Compound  Compound                                                                              mg/kg mg/l                                 Complex Weight   mol. weight                                                                             mg/kg fuel                                                                            fuel  fuel                                 ______________________________________                                        Example 3                                                                             40.08    634.92     951     60    50                                          (Ca)                                                                  Example 1                                                                             87.62    796.76    1023    131   110                                          (Sr)                                                                  ______________________________________                                    

The test conditions are given below in Table 2 together with theequivalent test mode of the ECE R49¹ 13 mode cycle.

                  TABLE 2                                                         ______________________________________                                        Engine Duty                                                                              R49 mode  Engine Speed rpm                                                                            Load, Nm                                   ______________________________________                                        Max torque (hill                                                                         6         1350          50                                         climb)                                                                        Max Power  8         2600          40                                         Max speed (light                                                                         11        2600          10                                         running)                                                                      ______________________________________                                    

Smoke emission was measured using the Bosch method ². In this method afixed volume of gas is drawn through a filter and the smoke valueobtained optically as a function of reduced reflectance.

Heat release was obtained using an AVL Indiskop ³ to record a number ofengine parameters from transducers on the engine. In particular cylinderpressure data is used in a computer model to estimate the quantity andtiming of heat release resulting from fuel combustion.

RESULTS

Smoke Measurement

These are recorded in Table 3 below. The figures in parentheses refer tothe number of test runs.

                  TABLE 3                                                         ______________________________________                                                     Base fuel  % Re-  Base fuel                                                                              % Re-                                              Plus Ca    duction                                                                              Plus Sr  duction                                    Base    Complex    in Bosch                                                                             Complex  in Bosch                              R49  fuel    (Example 3)                                                                              smoke  (Example 1)                                                                            smoke                                 ______________________________________                                        6    2.13(4) 1.12(1)    47     0.7(3)   67                                    8    2.63(4) 1.17(1)    56     2.17(3)  17                                    11   1.65(4) 0.5(1)     70     1.10(3)  33                                    ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                             Base Fuel plus                                                                            Base Fuel plus                                                    Ca Complex  Sr Complex                                              Base Fuel (Example 3) (Example 1)                                  ______________________________________                                        5% Heat release                                                                          -8.69     -8.51       -8.53                                        (deg BTDC)                                                                    10% Heat release                                                                         -8.14     -7.91       -7.93                                        (deg BTDC)                                                                    50% Heat release                                                                         -2.59     -1.51       -1.71                                        (deg BTDC)                                                                    90% Heat release                                                                         16.40     39.46       37.00                                        (deg BTDC)                                                                    ______________________________________                                        Footnotes:                                                                    1.  ECE R49 see:                                                                  European 13-Mode Cycle - 9037/86. Transposed into EEC                         COUNCIL DIRECTIVE 88/76EEC.                                               2.  Bosch smoke measurement see:                                                  0681 169 038 EFAW 65A                                                         0681 168 038 EFAW 68A                                                         Robert Bosch GmbH                                                             Stuttgart                                                                 3.  AVL 647 Indiskop see:                                                         Version MIP A/E 6.4 with supplement to                                        Version MIP A/E 7.0                                                           AVL List GmbH                                                                 Kleiss Strasse 48, A-8020                                                     Graz. Austria.                                                        

Vehicle Smoke Emission--DI Truck

These were carded out on a small commercial flat body truck equippedwith a standard optional Perkins NA Phaser diesel engine (specification:see Appendix 1). The fuel delivery system was modified to enable easyswitching between the test fuels with no inter-fuel contamination.

The base fuel used was a standard commercial UK Derv. (see Appendix 2).The smoke suppressant complex was first dissolved in a small volume (10ml) Shell Sol AB (aromatic kerosene solvent bp 210° C.) prior toaddition to the fuel in amounts sufficient to yield metal concentrationin the fuel of 1, 10 and 100 ppm.

All of these vehicle tests were made on a chassis or roller dynamometerthat had been set to simulate the road drag power of the truck. The testprocedures were as set out in the US Code of Federal Regulations. Title40. Part 86 and Part 600. Springfield, National Technical InformationService 1989.

Part 86 refers to the Urban drive schedule test, which consists of threephases. These are the Cold transient (CT), Stabilised (S) and Hottransient (HT) phases. FTP is used here to indicate the overall result,which is a weighed average of the three phases.

Part 600 refers to the Highway fuel economy test (HWFET). Here furtherabbreviated to (HW).

Operation of the truck and analysis of the exhaust emissions were, apartfrom the specification of the fuel and the measurement particulatesduring the HW. as set out in the US Code of Federal Regulations above.

The results are presented in Table 5 in which the followingabbreviations are used:

CT: Cold Transient Test. Engine run for 505 seconds after "cold soaking"the engine overnight at 20°-30° C.

S: Stabilised Test. Carried out immediately after the CT test and testsfor 866 seconds.

HT: Hot Transient Test. Carried out 10 minutes after the StabilisedTest.

The CT,S and HT tests include the US Federal Urban Drive Schedule, a3-phase test, details to be found in US Code of Federal Regulations,Title 40, Part 86.

FTP is the Federal Test Procedure, US Code of Federal Regulations, Title60, Part 600.

HW is a Highway drive cycle normally formed as part of the Highway FuelEconomy Test.

The results presented in Tables 3, 5 and 6 clearly show the fineparticle suppressant properties of the present compounds when added todiesel fuel and the reduction in hydrocarbon emission.

In the Tables, the particulate and unburnt hydrocarbon emission iscalculated and expressed as function of distance, i.e. g/km, and theresults given are the average of two runs.

                  TABLE 5A                                                        ______________________________________                                        Particulates Emission (g/km)                                                  (Additive = Sr Complex, Example 1)                                                       Base Fuel plus additive                                            Test  Base Fuel  1 ppm (Sr)                                                                              10 ppm (Sr)                                                                            100 ppm (Sr)                              ______________________________________                                        CT    0.248      0.216     0.223    0.226                                                      (-12.9%)  (-10.1%) (-8.9%)                                   S     0.222      0.214     0.205    0.215                                                      (-3.6%)   (-7.7%)  (-3.2%)                                   HT    0.237      0.228     0.244    0.256                                                      (-3.8%)   (+2.9%)  (+8.0%)                                   FTP   0.229      0.218     0.219    0.228                                                      (-4.8%)   (-4.4%)    (0%)                                    HW    0.119      0.103     0.118    0.103                                                      (-13.4%)  (-15.5%) (-13.4%)                                  ______________________________________                                    

                  TABLE 5B                                                        ______________________________________                                        Particulates Emission, (g/km) (Additive = Sr Complex                          (Example 1) plus K Complex (Example 2)                                        Test  Base Fuel  Base Fuel plus additive 10 ppm Sr and K                      ______________________________________                                        CT    0.248       0.217 (-12.5%)                                              S     0.222      0.222 (0%)                                                   HT    0.237      0.244 (+2.1%)                                                FTP   0.229      0.227 (-0.9%)                                                HW    0.119      0.113 (-5.0%)                                                ______________________________________                                    

                  TABLE 6A                                                        ______________________________________                                        Hydrocarbon Emission (g/km) (Additive = Sr Complex,                           Example 1)                                                                               Base Fuel plus additive                                            Test  Base Fuel  1 ppm (Sr)                                                                              10 ppm (Sr)                                                                            100 ppm (Sr)                              ______________________________________                                        CT    0.655      0.557     0.545    0.55                                                       (-15.0%)  (-16.8%) (-16.0%)                                  S     0.946      0.836     0.82     0.817                                                      (-11.6%)  (-13.3%) (-13.6%)                                  HT    0.588      0.538     0.53     0.535                                                       (-8.5%)   (-9.9%)  (-9.0%)                                  FTP   0.788      0.697     0.684    0.685                                                      (-11.5%)  (-13.2%) (-13.1%)                                  HW    0.353      0.358     0.326    0.363                                                       (+1.4%)   (-6.8%)  (+2.8%)                                  ______________________________________                                    

                  TABLE 6B                                                        ______________________________________                                        Hydrocarbon Emmission (g/km) (Additive = Sr Complex,                          Example 1 and K Complex, Example 2)                                           Test  Base Fuel  Base Fuel plus additive 10 ppm (Sr + K)                      ______________________________________                                        CT    0.655      0.518 (-20.9%)                                               S     0.946      0.731 (-22.7%)                                               HT    0.588      0.528 (-10.2%)                                               FTP   0.788      0.632 (-19.8%)                                               HW    0.353      0.346 (-2.0%)                                                ______________________________________                                    

                  TABLE 6C                                                        ______________________________________                                        Hydrocarbon Emission (g/km) (Additive = Ca Complex,                           Example 3)                                                                    Test   Base Fuel Base Fuel plus additive 10 ppm (Ca)                          ______________________________________                                        CT     0.655      0.577 (-11.9%)                                              S      0.946     0.858 (-9.3%)                                                HT     0.588     0.551 (-6.3%)                                                FTP    0.788     0.716 (-9.1%)                                                HW     0.353     0.368 (+4.2%)                                                ______________________________________                                    

Vehicle Smoke Emission Tests--Diesel Car

These were carried out on a Peugeot 309 car equipped with an XUD 9 IDIengine (specification: see Appendix 3). The fuel system of the vehiclehad been modified to enable easy switching between the test fuels withno interfuel contamination.

The baseful used was a standard commercial UK DERV (see Appendix 4). Thevarious additives evaluated were dissolved directly into diesel fuel inamounts sufficient to yield a metal concentration in the fuel of 10 ppm.

All of the vehicle tests were made on a chassis or roller dynamometerthat had been set to simulate the road drag power of the car. Exhaustparticulate samples were taken from a dilution tunnel using theprinciples specified in EC Directive, 91/441 EEC and US FTP testprocedures. The exhaust gas was sampled with the vehicle operating at 70kph constant speed for a distance equivalent to 12 km.

The weight increase of the filter papers following the test period werecalculated and reflect the emissions of particulate from the engine. Theresults give in Table 7 clearly show the benefits of the additives ofthis invention in reducing smoke emissions from motor vehicle dieselengines.

                  TABLE 7                                                         ______________________________________                                        Peugeot 309 XUD 9 IDI Engine Constant Speed of 70 kmph                                      Particulates                                                                          Mean     Reductions                                                   (g/km)  (g/km)   (%)                                            ______________________________________                                        Base    Run 1   12 km   0.0620  0.0622 0.0                                            Run 2   12 km   0.0626                                                        Run 3   12 km   0.0619                                                Additive                                                                              Run 1   12 km   0.0631  0.0615 1.1                                    Example 8                                                                             Run 2   12 km   0.0679                                                        Run 3   12 km   0.0535                                                Additive                                                                              Run 1   12 km   0.0529  0.0553 11.0                                   Example 2                                                                             Run 2   12 km   0.0577                                                        Run 3   12 km   0.0554                                                Additive                                                                              Run 1   12 km   0.0470  0.0440 29.3                                   Example 1                                                                             Run 2   12 km   0.0440                                                        Run 3   12 km   0.0409                                                Additive                                                                              Run 1   12 km   0.0523  0.0568 8.6                                    50/50   Run 2   12 km   0.0568                                                Example Run 3   12 km   0.0614                                                7/12                                                                          ______________________________________                                    

Static Engine Tests--Measurement of Smoke and Hydrocarbon Emissions

Tests were carried out to examine the smoke reducing effects of a numberof additives. The tests were made using the static Perkins 236 DI singlecylinder research engine. It was a direct injection design and wasnormally aspirated.

The engine exhaust was arranged to flow through a Celesco (Obscuritytype) smoke meter. Bosch smoke number of the exhaust gas was alsomeasured as a verification of the Celesco method, although thediscrimination of the Bosch method is less than that of the Celesco.

The unburned hydrocarbons in the exhaust were measured by samplingthrough a heated sample line to a Flame ionisation detector (FID). Thismeasured unburned exhaust hydrocarbons as Carbon 1 equivalent. (Methaneequivalent concentration in terms of parts per million volumes).

The fuel pump was a single plunger type and arrangements were made tochange fuel source without contamination of one fuel by another.

An engine test condition of 1350 rev/min equivalent to maximum torqueoperation (R49 mode 6) was chosen to compare the smoke effects of theadditised fuels with those of the same fuel without additive. The testprogramme was arranged so that the smoke meter reading of an untreatedbaseline fuel was measured before and after the smoke reading taken fromthe engine running with each candidate additised fuel. The benefit ofthe fuel additive could be determined by comparing the smoke value tothe average of the bracketing basefuel smoke values. The base fuel was astandard commercial UK Derv (see Appendix 4). The results of the testsare summarised in the following Table 8.

                  TABLE 8                                                         ______________________________________                                        PERCENT REDUCTION DUE TO ADDITIVE                                             Additive Bosch Smoke Celesco Smoke                                                                             Hydrocarbons                                 Example  Number      % Obscurity as CH.sub.4                                  ______________________________________                                         1       3.37        9.28        6.15                                                  8.59        7.11        10.06                                                 6.67        7.62        5.58                                          2       2.70        17.92       24.98                                         3       2.02        5.29        -3.37                                         7       4.62        13.76       20.60                                         8       5.26        11.77       14.21                                                 10.16       13.70       28.59                                        10       1.54        6.12        17.83                                        11       10.37       3.68        12.15                                        12       9.32        21.67       6.17                                         13       10.67       15.44       14.15                                        14       6.45        11.70       23.75                                        15       10.59       14.02       -15.07                                       1/8      3.94        9.36        23.31                                        (50/50)                                                                       ______________________________________                                    

                  APPENDIX 1                                                      ______________________________________                                        Make:            Renault 50 Series Truck                                      First Registered:                                                                              14th August 1990                                             Unladen Weight:  2341 Kg                                                      Max. Laden Weight:                                                                             3500 Kg                                                      Test Inertia Weight Used For                                                                   2438 Kg                                                      These Tests:                                                                  Perkins:         4.40 Q1                                                      Engine Capacity: 3990 cm.sup.3                                                Rated Power:     59.7 kW at 2800 rpm                                          Compression ratio:                                                                             16.5:1                                                       Bore:            100 mm                                                       Stroke:          127 mm                                                       Direct injection design                                                       Normally aspirated                                                            Fuel Pump Bosch type EPVE                                                     Transmission:    Rear wheel drive - (The outer of                                              the twin rear driving wheels was                                              removed for the dynamometer                                                   testing only. This is to allow the                                            wheels to fit within the dynam-                                               ometer rolls length).                                        Gearbox:         5 speed manual shift                                         Final drive ratio:                                                                             3.53:1                                                       ______________________________________                                    

                  APPENDIX 2                                                      ______________________________________                                        Density @ 15° C.                                                                          0.8379                                                     Viscosity @ 40° C.                                                                        2.842                                                      Cloud Point °C.                                                                           -3                                                         CFPP °C.    -22                                                        Pour Point °C.                                                                            -22                                                        Flash Point °C.                                                                           67                                                         Sulphur % wt. %    0.184                                                      FIA: -                                                                        % vol. Saturates   64.4                                                       % vol. Olefins     2.4                                                        % vol. Aromatics   33.2                                                       Distillation. IBP @ °C.                                                                   168                                                         5% vol. @ °C.                                                                            198                                                        10% vol. @ °C.                                                                            212                                                        20% vol. @ °C.                                                                            234                                                        30% vol. @ °C.                                                                            251                                                        40% vol. @ °C.                                                                            265                                                        50% vol. @ °C.                                                                            276                                                        65% vol. @ °C.                                                                            292                                                        70% vol. @ °C.                                                                            298                                                        85% vol. @ °C.                                                                            322                                                        90% vol. @ °C.                                                                            334                                                        95% vol. @ °C.                                                                            353                                                        FBP @ °C.   369                                                        % vol. Recovery    98.5                                                       % vol. Residue     1.4                                                        % vol. Loss        0.1                                                        Cetane Number      50.3                                                       Cetane Improver    NIL                                                        ______________________________________                                    

                  APPENDIX 3                                                      ______________________________________                                        Make             Peugeot 309 1.9 diesel                                       First Registered 15th February 1989                                           Unladen wt.      904 kg                                                       Engine type      XUD9 Type 162.4/OHC                                          Engine capacity  1905 cm.sup.3                                                Rated power      47 kW @ 4600 rev/min                                         Compression ratio                                                                              23.5:1                                                       Bore             83 mm                                                        Stroke           88 mm                                                        Fuel pump        CAV rotodiesel DPC 047                                       Transmission     Front wheel drive                                            Gear box         5-speed (manual)                                             Registration     F798 JCA                                                     Engine No.       162 - 140898                                                 Injecter Assembly                                                                              CAV LCR 67307                                                Injecter nozzle  RDNG SDC 6850                                                ______________________________________                                    

                  APPENDIX 4                                                      ______________________________________                                        Density @ 15° C.                                                                          0.8373                                                     Viscosity @ 40° C.                                                                        2.988                                                      Cloud Point, °C.                                                                          -3                                                         CFPP, °C.   -17                                                        Pour Point, °C.                                                                           -21                                                        Flash Point, °C.                                                                          67                                                         Sulphur, % wt      0.17                                                       FIA analysis                                                                  % vol Saturates    73.2                                                       % vol Olefins      1.3                                                        % vol Aromatics    25.5                                                       Distillation, IBF @ °C.                                                                   177                                                         5% vol @ °C.                                                                             200                                                        10% vol @ °C.                                                                             213                                                        20% vol @ °C.                                                                             237                                                        30% vol @ °C.                                                                             255                                                        40% vol @ °C.                                                                             269                                                        50% vol @ °C.                                                                             280                                                        65% vol @ °C.                                                                             296                                                        70% vol @ °C.                                                                             301                                                        85% vol @ °C.                                                                             324                                                        90% vol @ °C.                                                                             335                                                        95% vol @ °C.                                                                             351                                                        FBP @ °C.   364                                                        % vol Recovery     98.6                                                       % vol Residue      1.4                                                        % vol Loss         0.0                                                        Cetane Number      52.3                                                       Cetane Improver, % NIL                                                        ______________________________________                                    

We claim:
 1. An additive composition for liquid hydrocarbon fuelseffective to reduce particulate emission when the fuel is burned and/orreduce unburnt hydrocarbon emission, the additive composition comprisingone or more oil-soluble Lewis base metallo-organic complexes consistingof the formula M(R)_(m).nL whereM is the cation of an alkali metal, analkaline earth metal, or a rare earth metal of valency m, not all metalcations (M) in the complex necessarily being the same; R is the residueof an organic compound RH, where R is an organic group containing anactive hydrogen atom H replaceable by the metal M and attached to an O,S, N or C atom in the group R, that R group containing an electronwithdrawing group adjacent or close to the O, S, N or C atom carryingthe active H atom and being in a position to form a dative bond, in saidcomplex, with the metal cation M, but not including active hydrogenatom(s) forming part of a carboxyl group (COOH); n is a positive numberindicating the number of donor ligand molecules forming a dative bondwith the metal cation, but which can be zero when M is a rare earthmetal cation; and L is an organic donor Ligand (Lewis base); in solutionin an organic carrier liquid miscible in all proportions with the fuel.2. An additive composition according to claim 1, where M in said formulais the cation of an alkali or alkaline or rare earth metal.
 3. Anadditive composition according to claim 2, where M in said formula isLi, Na, K, Sr, Ca or Ce.
 4. An additive composition according to claim1, where R is an organic group of from 1-25 carbon atoms.
 5. An additivecomposition according to claim 4 wherein the electron-withdrawing groupin the organic group R is a hetero atom or group consisting of orcontaining as the hetero atom O, S or N.
 6. An additive compositionaccording to claim 5, where the electron withdrawing group in R is C═O,C═S or C═NH.
 7. An additive composition according to claim 4 where R isthe residue of a β-diketone.
 8. An additive composition according toclaim 1, where R is the residue of a β-diketone of the formula

    R.sup.1 C(O)CH.sub.2 C(O)R.sup.1

where R¹ is a substituted or unsubstituted C₁ -C₅ alkyl group, C₃ -C₆cycloalkyl, phenyl, C₁ -C₅ substituted phenyl, or benzyl, the R¹ groupsbeing the same or different.
 9. An additive composition according toclaim 5 where R is the residue of a heterocyclic group containing an##STR3## group as part of the heterocycle, where Y is O, S or NH.
 10. Anadditive composition according to claim 1, wherein R is a phenolicresidue.
 11. An additive composition according to claim 10, wherein R isthe residue of a substituted phenol containing from 1 to 3 substituentsselected from alkyl, alkoxy, aminoalkyl and alkylaminoalkyl groups offrom 1 to 8 carbon atoms.
 12. An additive composition according to claim1, where n is 1, 2, 3 or
 4. 13. An additive composition according toclaim 1, where L is HMPA, TMEDA, PMDETA, DMPU or DMI.
 14. An additivecomposition according to claim 1, wherein the carrier liquid is anaromatic solvent.
 15. An additive composition according to claim 1containing from 0.1 to 50% by wt. of the metal(s) M.
 16. A liquidhydrocarbon fuel containing a Lewis base metallo-organic coordinationcomplex of the formula defined in claim 1, in an amount sufficient toprovide from 0.1-100 ppm of the metal M in said fuel.
 17. A fuelaccording to claim 16 which is a distillate hydrocarbon fuel.
 18. A fuelaccording to claim 17, which is a diesel fuel.
 19. A fuel according toclaim 17, which is a heating oil.
 20. A method of reducing theparticulate emissions from liquid hydrocarbon fuels, which comprisesincorporating into the fuel prior to combustion an alkali, alkalineearth or rare earth metal complex of the formula defined in claim 1, ora mixture of two or more such complexes in an amount sufficient toprovide in said fuel from 0.1 to 100 ppm of the metal(s) M.
 21. A methodof reducing the unburnt hydrocarbon emission of liquid hydrocarbon fuelswhen combusted, which comprises incorporating into the fuel prior tocombustion an alkali, alkaline earth or rare earth metal complex of theformula defined in claim 1, or a mixture of two or more such complexesin an amount sufficient to provide in said fuel from 0.1 to 100 ppm ofthe metal(s) M.
 22. A method of reducing carbon deposits resulting fromthe incomplete combustion of liquid hydrocarbon fuels, which comprisesincorporating into the fuel prior to combustion an alkali, alkalineearth or rare earth metal complex of the formula defined in claim 1, ora mixture of two or more such complexes in an amount sufficient toprovide in said fuel from 0.1 to 100 ppm of the metal(s) M.